mb_explode() function

mb_explode.function.php

<?php
/*
 * Copyright (C) 2012 by HiNa <hina@bouhime.com>. All rights reserved.
 *
 * LICENSE
 *
 * This source file is subject to the 2-clause BSD License(Simplified
 * BSD License).
 */
if(!function_exists('mb_explode')) {
    function mb_explode($delimiter, $string, $limit = -1, $encoding = 'auto') {
        if(!is_array($delimiter)) {
            $delimiter = array($delimiter);
        }
        if(strtolower($encoding) === 'auto') {
            $encoding = mb_internal_encoding();
        }
        if(is_array($string) || $string instanceof Traversable) {
            $result = array();
            foreach($string as $key => $val) {
                $result[$key] = mb_explode($delimiter, $val, $limit, $encoding);
            }
            return $result;
        }

        $result = array();
        $currentpos = 0;
        $string_length = mb_strlen($string, $encoding);
        while($limit < 0 || count($result) < $limit) {
            $minpos = $string_length;
            $delim_index = null;
            foreach($delimiter as $index => $delim) {
                if(($findpos = mb_strpos($string, $delim, $currentpos, $encoding)) !== false) {
                    if($findpos < $minpos) {
                        $minpos = $findpos;
                        $delim_index = $index;
                    }
                }
            }
            $result[] = mb_substr($string, $currentpos, $minpos - $currentpos, $encoding);
            if($delim_index === null) {
                break;
            }
            $currentpos = $minpos + mb_strlen($delimiter[$delim_index], $encoding);
        }
        return $result;
    }
}

Sorry, but if I use the PHP instructions:
ini_set('display_errors', 1); error_reporting(E_ALL);

in such code (for example):
$cSimple_String = 'Hello word';
$cDelim = "";
$aSimple_Array = mb_explorer( $cDelim, $cSimple_String );

I receive a warning error:
Warning: mb_strpos() [function.mb-strpos]: Empty delimiter in mb_explode.function.php on line 33
33 if(($findpos = mb_strpos($string, $delim, $currentpos, $encoding)) !== false) {